Underground gas storage
Natural gas is mainly stored in porous (i.e. aquifer) reservoirs or cavern reservoirs, which are filled during the warmer months when the demand for gas is low. When the weather turns colder, they are emptied to satisfy the higher demand. Porous reservoirs usually cover the seasonal base load, often in combination with cavern reservoirs, which are particularly suitable for covering peak demand at specific times of the day.
On account of the natural flow paths in the reservoir rock, porous reservoirs are slower in their response to changes in production rates than cavern reservoirs, which are more comparable to an underground pressure vessel. According to the International Gas Union, there is an installed working gas volume of around 333 billion m3 available worldwide in more than 600 underground gas reservoirs.
Although about 70% of these reservoirs are in the United States and 25% in Europe, Europe's reservoirs account for about 60% of the installed working gas volume and those in the United States only about 35%.